Electro hydraulic servovalve

ABSTRACT

An electrohydraulic servovalve including a signal responsive torque motor having at least one high energy permanent magnet providing a magnetic flux field. A flux field shunt is affixed to the magnet to compensate for the effects of temperature on servovalve operating characteristics to ensure a consistent hydraulic output function in relation to a given input signal over a wide range of operating temperatures.

United States Patent I Inventor Donald A. King Camarillo, Calif.

Appl. No. 823,877

Filed May 12, 1969 Patented Jan. 19, 1971 Assignee Borg WarnerCorporation Chicago, II]. a corporation of Delaware ELECTRO HYDRAULICSERVOVALVE 8 Claims, 5 Drawing Figs.

US. Cl. l37/625.4, 1 37/625.62; 335/217, 335/236- Int. Cl ..Fl6lt 31/04,H02k 33/ 12 Field ofSearch ..137/625.65,

625.62, 625.4; 335/217, 236; 310/36, 29, (Inquired), 214, 216

[56] References Cited 3 UNITED STATES PATENTS 1,632,609 6/1927 Lee335/217 2,720,603 [0/1955 Mitchell et a1. 335/2 1 7X 2,961,002 1 1/ 1960Gordon 137/625'.62 3,154,728 10/1964 Bordenet... 335l236X 3,194,9986/1965 Marfut 335/217X 3,415,283 12/1968 Trbovich et a1 l37/625.62

Primary Examiner-M. Cary Nelson Assistant Examiner-R. B. RothmanAttomeys-Donald W. Banner, Lyle S. Motley, C. G. Stallings and WilliamS. Mc Curry ABSTRACT: An electrohydraulic servbvalve including a signalresponsive torque motor having at least one high energy permanent magnetproviding a magnetic flux field. A flux field shunt is affixed to themagnet to compensate for the effects of temperature onservovalveoperating characteristics to ensure a consistent hydraulicoutputfunction in relation to a giveninput signal over a wide range ofoperating temperatures.

PATENTEUJAMQBTI" 3.5561150.

SHEET 2 [1P2 v ivsa 5v W M). Wm

ATTORNEY I 1,-ELECTRQ'HYDRAULICSERVOV-ALVE BAcxoRouND or Tl-IEINVENTIONThe invention relates to electrohydraulic servovalves. More Iparticularly, it relates to electrohydraulic-'servovalves having meansto compensate for: the effects of temperature on servovalve operatingcharacteristics. Electrohydraulic servovalves are used to'translate' alow energy electrical-input .to a high energy hydraulic output.Servovalv'es in many applications are exposed to a-widerange ofoperating temperatures. Under such conditions, it is typical toexperience a gradual degradationin servovalve output at any givenelectrical input asoperating temperature increases. .This

phenomenon is attributedto a'grean'extent to the thermal characteristicsof the high energy permanent magnets commonly used in these devices. f

, The effect of temperature on the remanence of a permanent magnetmanifestsitselfin two different ways: 1 l.-The nonreversible effect; and

2.The-reversibleeffect.;.- L 1 'Theformerproduce's "a loss in theremanentflux' density, which when certaintemperature extremes "areencountered cannot be restored. "This 'nonreversible effect can beeliminated by the simple expedient of. cycling the magnet several timesthroughttheant'icipatedrange before finally adjustingitsoperatingfluxdensity. I v

The reversible effect cannot be eliminated, however, and servovalve.operating characteristics are affected by the degradation of themagnetic fluxgfield astemperatureim creases.

Ina servovalvepincreased operating temperature not only affectsthemag'ne tic characteristics of thetorque motor, but also producessignificant changes in-valve orificeand pumping characteristics due tomechanical thermal expansion.

It is essential .to reliable servovalve performance to minimize thevariations ino'utput signal in relation to varying temperatureconditions. It has beendetermined that. compensation fortheefi'ects oftemperature oh'thevarious operating characteristics may beprovidedbycontrol of the flux density of the permanent magnets/formingpart of the servovalve torque motor. lnthis way, asinglecompensationmeansovercomes the undesirable variations in' operatin'gcharacteristics of theservovalveeomponents.

1 Accordin'gly,:i,t is thejprincipal object 6:- the .presentinvention toprovidean electrohydraulic servovalve which includes means forcompensating for the effects of temperature upon all of the operatingvariables affected by changesin'operating temperature to produce aconsistent hydraulic output function in relation to given electrical,input'command.

, SUMMARY OF THE INVENTION Very generally, the electrohydraulicservovalve of the present invention includes atorque motor responsive toan electrical input signal to control an hydraulic output function.

The hydraulic output function is variable in response to the inputsignal. The servovalve includes a-torque motor having at least onepermanent magnet to establish aflux'field. A magnetic shunt'is affixedto the permanent magnet which produces an inverse characteristicof gainin'relation to increasingtemperature to compensate-for the'effects oftemperature upon the servovalve operating parameters including loss ofmagnetization, mechanical and thermal expansion, orificecharacteristics, and pumping effects,

The compensator is affixed tothe magnet in contact with the maximumpotential portions of the magnet and is shaped I to provide maximumcontact with the magnet to provide optimum compensating efficiency. 'Atlow temperature,a portion of the magnetic flux field produced by themagnet is bypassed through the compensator. As temperature increases,

the efficiency of the compensator, because of its inherent.

characteristic of inverse gain, is reduced. As temperature increases, anincreased proportion of magnetic flux is released into the activemagneticeircuit to compensate for the overall degradation of theavailable flux field as well as the other operating variables affectedby the increased temperature.

More particular objects and advantages of the present invention willbecome apparentin' connection with the following description havingreference to theaccomp'anying drawings.

DESCRlPTlON OF THE DRAWlNGS FIG. 1 is a sectional elevationalview inpartial schematic of an electrohydraulic servovalve illustrative ofprinciples of the l l't'fsent-inv'ention.

FIG. 2 isaside elevational sectional view of the apparatus of FIG. ltalten generally along the line 2-2 of that FIG.

FIG. '3 is a perspective view of a portion of the apparatus of FIG. 1illustrating a torque motor permanent magnet and attach'e d compensator.a

FIG. 4 is a diagrammatic view of a portion of the apparatus of FIG. 1illustrating conditions existing at low temperature. FIG. 5 is adiagrammatic view of a portion of the apparatus of FIG. 1 illustratingconditions existing at high temperature.

" DETAILED-DESCRIPTION i I Referringspecifically to the drawings, thereis illustrated an facing, spaced apart relation.

A pair f orifice elements 21 are'dispos ed withinthe valve body anddefine fixed orifices '22 spaced outwardly of the noz- .zles' inadirection away from the vertical passage 17. Passages '25 provide fluidcommunication between the orifices 22 and the nozzles 19. V

Hydraulic fluid under pressure in the order of magnitudeof 3,000 psi. isapplied to theiservovalveby a hydraulic supply pump (not shown). Thisfluid enters'the valve body and is 'divided' intoa pair of inlet orsupplyjpassages 27. This fluid passes 4 through the nozzles 22 into thepassages 25. Each passage 25 is in communication with an output passage29.

These passages are, in turn, connected to the actuator 15 and fluid,flow through the outlet passages. accomplishes the desired movementofthe actuator in-response to the input signal. The passages 25 areadditionally in communication with the sump of the supply pump throughthe nozzles 19 and the vertical passages 17.

Disposed within the vertical passage 17 is a flapper 31. The flapperincludes a support ring 33 secured to the valve body 13 in fluid tightrelation. This support ring is provided with a flexible diaphragm (notshown) which provides a flexible, fluid tight seal between the valvebody 13 and the torque motor 11. I The portion of the flapper 31extending into the vertical passage includesa flattened end portion 35disposed between the nozzles 19 in juxtaposed, spaced apart relation tothe nozzle openings. The flapper further includes a portion 37 extend- 7ing into the torque .motor 11 which includes an integrally formedtransverse armature 39 of magnetic material which forms the armature ofthe torque motor 11.

The passages 29 communicate hydraulic output of the servovalve to theactuator 15 through passages or conduits 41. The actuator 15 includes ahollow cylinder 43 within which is disposed a reciprocable piston 45.The piston is secured to an output shaft 47 which extends outwardly ofthe cylinder and is connected to a mechanical linkage, and impartsmovement to the linkage in response to the servovalve operation.

direction. Conversely theflow of fluid through the other of the passages29 and conduit 41 into the cylinder 43 causes movement of the piston 45and output shaft 47 in the opposite direction. In this way, movement ofthe mechanical linkage may be readily accomplished in response to thehydraulic flow in the servovalve.

The torque motor 11 is secured to the main valve body 13 in overlyingrelation to the flapper 31. A cover member 49 surrounds the torquemotor.

The torque motor includes a pair of permanent magnets 53 supported invertically disposed spaced apart relation between a pair of generallyhorizontal pole pieces 55. The magnets are horizontally elongated andhave poles or maximum potential portions in contact with the polepieces.

As seen in FIG. 1 the pole pieces include upwardly and downwardlydirected end portions 57 terminating in closely spaced relation definingworking air gaps associated with opposite ends of the armature 39 of theflapper 31. The pole pieces direct the flux field established by thepermanent magnets across the gaps between the facing end portions and\thereby establish a concentrated magnetic field associated with theflapper armature (see F [68.4 and The torque motor 11 additionallyincludes a pair of electrical coils 59 and 61. Each coil is disposed insurrounding relation to a portion of the armature 39 on opposite sidesof the flapper. These coils are connected to a source of electricalinput signal (not shown) which established an electromagnetic flux feld.

Opposite ends of the armature 39 are each subjected to two magnetic fluxfields, one established by the permanent magnets and concentrated uponthe armature ends by the pole pieces 55 and one established byelectrical coils 59 and 61. By controlling the current flow to eachcoil, a differential flux is produced which will cause movement of thearmature in either the clockwise or counterclockwise direction. Thiswill in turn cause a corresponding movement of the flattened end portion35 of the flapper toward one of the nozzles 19 and away from the otherprogressively inhibiting flow through one nozzle opening andprogressively increasing flow through the other. Inhibiting flow throughone nozzle causes a corresponding increase in the flow through theassociated outlet passage 29 in conduit 41 into the actuator cylinder43. An increase in flow through the opposite nozzle causes flow from thecylinder 43 through the opposite conduit.4l in passage 29 into thepassage 25 and through the nozzle opening to the sump. This actioncauses movement of the piston 45 and output shaft 47 in one direction orthe other, depending upon the direction of movement of the flattened endportion 35. Equalization of the current flow in the coils 59 and 61returns the flapper flattened end portion 35 to the neutral positionresulting in an equal flow through each nozzle opening. At that pointmovement of the piston 45 is terminated. I

In accordance with the present invention and as best seen in FIG. 3,compensating means are provided in the torque motor to ensure consistenthydraulic output in relation to a given input signal command. Thecompensating means includes a pair of shunts 63 secured to the permanentmagnets 53 which provide the initial or constant flux field of thetorque motor 1 l The shunt 63 is essentially rectangular in shape and itincludes opposite end portions 65 which are deformed slightly in adirection toward the magnet to which it is affixed to insure intimatecontact with the end portions of the shunt with the areas of maximumpotential of the magnet.

In the illustrated embodiment the shunts 63 are secured to the permanentmagnets 53 by a spot weld 67 intermediate the poles of the magnet in thearea of minimum potential. It must be appreciated that any suitablemeans for fastening the compensator may be utilized so long as intimatedirect contact between the compensator and the magnet in the areasofmaximum potential of the magnet is achieved.

The compensator is formed of any suitable permeable material such as,for example, nickel-iron alloy which has a high permeability and lowtemperature and suffers a loss of permeability as temperature increases,thus reducing its ability to divert magnetic flux.

FIGS. 4 and 5 illustrate the operation of the compensators 63. While inthe illustrated embodiment one such compensator 63 is attached to eachone of the permanent magnets 53, it must be appreciated that in certainapplications only one compensator attached to one magnet need be usedwithout in any way departing from the scope of the invention.

As illustrated, the compensators or shunts 63 attached to the magnets 53present a high permeability path between the areas of maximum potentialof the magnets at low operating temperatures. As a result thecompensators bypass or divert a relatively large amount of magnetic fluxfrom the pole pieces 55 and consequently from the working air gapbetween the pole piece end portions 57. This arrangement establishes themaximum flux field provided by the permanent magnetsto which the endportions of the armature 39 are subjected. As the temperature of theservovalve increases the magnetic field of the permanent magnets 53inherently decreases. Simultaneously the permeability of the shunt orcompensator 63 also decreases and is therefore less effective to bypassflux from the pole pieces 55 and working air gap between the endportions 57 of the pole pieces.

By selecting shunts of proper size and shape the-flux across the workingair gap may be maintained at a constant value and the servovalve canthus deliver a constant output regardless of the operating temperaturesexperienced. The shunt is sized to not only compensate for thedegredation of the magnetic field of the permanent magnets 53 inrelation to increasing temperature, but also is sized to compensate forthe variation in other operating characteristics of the valve such asorifice characteristics, mechanical thermal expansion and pumpingeffects. Thus by utilizing a single compensating arrangement the effectsof temperature upon all servovalve components is minimized andconsistent output in response to the given input signal is assuredthroughout a wide range of operating temperatures.

In a specific example of an electrohydraulic servovalve of the typedescribed a range of operating temperatures from between 20 F. to 320 F.was experienced. It was determined that the servovalve experienced anaverage gain, that is, change in hydraulic output function in relationto a given electrical input command in the order of l0percent at 320 F.and+5 percent at 20 F. as referenced to the gain experienced at atemperature of F. This gain was attributable to the variations inmagnetic, hydraulic and mechanical characteristics of the servovalve inrelation to variations in operating temperature. Since the compensatorproduces an inverse gain curve that is, it experiences a reduction inthe ability to bypass magnetic flux as temperature increases, attachmentofthe magnet shunt to the permanent magnets result in the establishmentof a constant hydraulic output function in response to a givenelectrical input signal over the entire operating range. A compensatorof generally rectangular shape formed of Carpenter (RegisteredTrademark) 032 alloy of a metal thickness of .020 inch was determined toprovide the necessary compensating capabilities. One such compensatorwas attached to each of the permanent magnets of the servovalve. Thecompensator was formed of rectangular shape to ensure that sufficientcontact area between the compensator and the maximum potential portionsof the magnet was provided. In this regard a contact area extending fromthe polarity extremes of the magnet to 25 percent of the distance to itsneutral magnetic zone was provided.

As can be seen an electrohydraulic servovalve has been provided whichproduces a consistent hydraulic output function in relation to a giveninput signal over a wide range of operat- '5 ing temperatures. Thecompensator accommodates variations in magnetic, hydraulic andmechanical characteristics of the valve in relation to variations intemperature.

Various features of the invention have been particularly shown anddescribed. However, it must be appreciated that various modificationsmay be made without departing from the scope of the invention.

lclaim: v

1. An electrohydraulic servovalve including a main valve body defining adivided fluid path, a pair of nozzles disposed in spaced apart facingrelation, each one of said nozzles being in fluid communication with aseparate portion of said fluid path, a flapper having an end portionpositioned intermediate said nozzles and movable toward and away fromeach said nozzle to control the flow of fluid in each portion of saiddivided flow path, said flapper including an opposite end defining anarmature, and a torque motor secured to said valve body to effectmovement of said flapper, said torque motor including at least onepermanent magnet to provide a permanent magnet flux field acting uponsaid armature, and at least one electric coil responsive to anelectrical input signal to provide a variable flux field acting uponsaid armature to vary the position of said flapper, said torque motorincluding at least one compensating shunt made of permeable materialaffixed to said permanent magnet in contact therewith to bypass aportion of said permanent magnet flux field at low temperature and beingresponsive to temperature to reduce the amount of flux bypassed astemperature increases.

2. An electrohydraulic servovalve as claimed in claim 1 wherein saidcompensating shunt is in contact with said permanent magnet at themaximum potential portion of said mag net.

3. An electrohydraulic servovalve as claimed in claim 2 wherein saidcompensating shunt is generally rectangular and includes opposite endportions deformed slightly in a direction toward said magnet and whereinsaid shunt is affixed to said magnet with said deformed end portionsthereof in contact with the maximum potential portions of said magnet.

4. An electrohydraulic servovalve as claimed in claim 1 wherein saidtorque motor includes a pair of permanent magnets disposed in spacedapart relation, a pair of pole pieces of magnetic material contactingsaid magnets at the maximum potential portions thereof, said pole piecesincluding opposite end portions disposed in facing spaced relationdefining air gaps therebetween and a portion of said armature of saidflapper is disposed in said air gap, said torque motor further includinga pair of said electrical coils each one of said coils surrounding aportion of said armature adjacent said portions thereof disposed in oneof said air gaps, and a pair of said compensating shunts, each one ofwhich is affixed to one of said permanent magnets.

5. A torque motor for an electrohydraulic servovalve having a flappermovable to control the flow of fluid therethrough including an armature,said torque motor including at least one permanent magnet to provide apermanent magnet flux field acting upon the armature and at least oneelectric coil responsive to an electrical input signal to provide avariable flux field acting upon the armature, said torque motorincluding at least one compensating shunt made of permeable materialaffixed to said permanent magnet in contact therewith to bypass aportion of said permanent magnet flux field at low temperature and beingresponsive to temperature to reduce the amount of flux bypassed astemperature increases. 1

6. A torque motor as claimed in claim 5 wherein said compensating shuntis in contact with said permanent magnet at the maximum potentialportions of said magnet.

7. A torque motor as claimed in claim 6 wherein said compensating shuntis generally rectangular and includes opposite end portions deformedslightly in a direction toward said magnet and wherein said shunt isaffixed to said magnet with said deformed end portions thereof incontact with the maximum potential portions of said magnet.

8. A torque motor as claimed in claim 5 wherein said torque motorincludes a pair of permanent magnets disposed in spaced apart relation,a pair of pole pieces of magnetic material contacting said magnets atthe maximum potential portions thereof, said pole pieces includingopposite end portions disposed in facing spaced relation defining airgaps therebetween and a portion of said armature of said flapper isdisposed in each said air gap, said torque motor further including apair of said electrical coils each one of said coils surrounding aportion of said armature adjacent said portions thereof disposed in oneof said air gaps, and a pair of said compensating shunts, each one ofwhich is affixed to one of said permanent magnets.

1. An electrohydraulic servovalve including a main valve body defining adivided fluid path, a pair of nozzles disposed in spaced apart facingrelation, each one of said nozzles being in fluid communication with aseparate portion of said fluid path, a flapper having an end portionpositioned intermediate said nozzles and movable toward and away fromeach said nozzle to control the flow of fluid in each portion of saiddivided flow path, said flapper including an opposite end defining anarmature, and a torque motor secured to said valve body to effectmovement of said flapper, said torque motor including at least onepermanent magnet to provide a permanent magnet flux field acting uponsaid armature, and at least one electric coil responsive to anelectrical input signal to provide a variable flux field acting uponsaid armature to vary the position of said flapper, said torque motorincluding at least one compensating shunt made of permeable materialaffixed to said permanent magnet in contact therewith to bypass aportion of said permanent magnet flux field at low temperature and beingresponsive to temperature to reduce the amount of flux bypassed astemperature increases.
 2. An electrohydraulic servovalve as claimed inclaim 1 wherein said compensating shunt is in contact with saidpermanent magnet at the maximum potential portion of said magnet.
 3. Anelectrohydraulic servovalve as claimed in claim 2 wherein saidcompensating shunt is generally rectangular and includes opposite endportions deformed slightly in a direction toward said magnet and whereinsaid shunt is affixed to said magnet with said deformed end portionsthereof in contact with the maximum potential portions of said magnet.4. An electrohydraulic servovalve as claimed in claim 1 wherein saidtorque motor includes a pair of permanent magnets disposed in spacedapart relation, a pair of pole pieces of magnetic material contactingsaid magnets at the maximum potential portions thereof, said pole piecesincluding opposite end portions disposed in facing spaced relationdefining air gaps therebetween and a portion of said armature of saidflapper iS disposed in said air gap, said torque motor further includinga pair of said electrical coils each one of said coils surrounding aportion of said armature adjacent said portions thereof disposed in oneof said air gaps, and a pair of said compensating shunts, each one ofwhich is affixed to one of said permanent magnets.
 5. A torque motor foran electrohydraulic servovalve having a flapper movable to control theflow of fluid therethrough including an armature, said torque motorincluding at least one permanent magnet to provide a permanent magnetflux field acting upon the armature and at least one electric coilresponsive to an electrical input signal to provide a variable fluxfield acting upon the armature, said torque motor including at least onecompensating shunt made of permeable material affixed to said permanentmagnet in contact therewith to bypass a portion of said permanent magnetflux field at low temperature and being responsive to temperature toreduce the amount of flux bypassed as temperature increases.
 6. A torquemotor as claimed in claim 5 wherein said compensating shunt is incontact with said permanent magnet at the maximum potential portions ofsaid magnet.
 7. A torque motor as claimed in claim 6 wherein saidcompensating shunt is generally rectangular and includes opposite endportions deformed slightly in a direction toward said magnet and whereinsaid shunt is affixed to said magnet with said deformed end portionsthereof in contact with the maximum potential portions of said magnet.8. A torque motor as claimed in claim 5 wherein said torque motorincludes a pair of permanent magnets disposed in spaced apart relation,a pair of pole pieces of magnetic material contacting said magnets atthe maximum potential portions thereof, said pole pieces includingopposite end portions disposed in facing spaced relation defining airgaps therebetween and a portion of said armature of said flapper isdisposed in each said air gap, said torque motor further including apair of said electrical coils each one of said coils surrounding aportion of said armature adjacent said portions thereof disposed in oneof said air gaps, and a pair of said compensating shunts, each one ofwhich is affixed to one of said permanent magnets.